The core devs were all paid to work on it when I was still active.

Not sure how many of the gnome (mutter) people are paid. Last I checked, the nvidia support was donated by nvidia (paid) for both KDE and Gnome.

I think KDE got some work sponsored by valve (before gamescope), though I'm not quite sure on that.

Overall, outside the sway/wlroots group I was a part of at the time, people generally worked adjacent or directly on wayland for day jobs.